Remove downlit to use built-in Quarto functionality instead

[vincentarelbundock]

#278

This simplifies code and maintenance for altdoc

The autolink argument is removed, but was never on CRAN so it is not really a "breaking change".

[etiennebacher]

I lost track of whether this ever worked for other tools than Quarto but .autolink() also applies downlit when the tool is not Quarto. Are we sure we're not losing functionalities here?

[vincentarelbundock]

We are losing "functionality" (in quotes), but there was always a big caveat in the docs:

Note that the autolink argument works best for Quarto-based websites. mkdocs appears to ignore downlit annotations altogether. docute and docsify display downlit annotations, but CSS styling and code highlighting sometimes suffer.

And that's with me only testing other outputs very minimally. Honestly, that functionality always felt really half-baked to me, and I'd feel more comfortable not shipping it at all rather than having something we know doesn't work super well. Especially, when the path to improvement is not clear, and it's doubtful either of us will invest a lot of work on downlit+docsify.

[etiennebacher]

Sounds good to me. Also, as you said autolink never made it to CRAN so it's not really a loss